1. Field of the Invention
The present invention generally relates to packer and sealing devices of the type used within a wellbore.
2. Description of the Related Art
There are generally two separate categories of designs for elastomeric wellbore packer seals: those that are set by axial compression and those that are set by moving the seal element radially outwardly with a ramp. Both of these designs are problematic when used at extreme wellbore depths wherein there are very high pressures and temperatures which tend to degrade elastomers. A compression set packer seal is compressed axially, which causes the seal element to expand radially until it contacts and seals against the inner radial surface of the surrounding casing or other tubular member. Compression set packers inherently require large volumes of elastomer, which is very expensive. In addition, it may be difficult or impossible to mold compression set packer elements from certain specialized elastomers that are resistant to high temperatures and pressures. Also at high pressures, the elastomeric seal element may become too soft to properly deploy anti-extrusion devices which prevent the elastomer from bleeding out along the axial space between the packer and the surrounding tubing.
Ramp set packer elements typically require the elastomeric sealing element to be bonded to a steel insert. But it is currently not feasible to bond elastomers that are greatly resistant to high temperatures and pressures to such inserts. Ramp set seals also have a tendency to leak when pressure is applied to the side with the smaller cross-section because the pressure pushes the seal element down the ramp. Even when a ratchet mechanism is used to try to retain the seal element on the ramp, there is still some inherent slippage that occurs.